1. Field of the Invention
The present invention relates to a transmission apparatus for outputting input data as a transmission signal. More specifically, the present invention is directed to a transmission apparatus and a communication system using the transmission apparatus, in which even when a characteristic value is changed which should be set as to a transmission signal, the transmission apparatus and the communication system are capable of being properly adapted to the change of the characteristic value to be set in a flexible manner without altering a circuit arrangement of the transmission apparatus.
2. Description of the Related Art
Very recently, while various sorts of communication methods such as wireless LANs (Local Area Networks) have been used, power line communications capable of utilizing power lines as network transfer paths have been proposed (for example, Japanese Laid-open Patent Application No. 2000-165304). In these communication methods, characteristic values indicative of physical characteristics (for instance, frequency bands and power levels) as to transmission signals outputted from transmission apparatus have been restricted based upon various sorts of laws (for instance, Japanese “DEMPA” law). The contents of these restrictions are made different from each other in correspondence with areas such as “counties.” Thus, technical specifications of these transmission apparatus have seen previously set in such a manner that characteristic values of transmission signals may be properly adapted to contents of restrictions established in correspondence with use areas.
However, while characteristic values which should be set are not always constant, there are some cases that these characteristic values are changed due to alterations of restricted contents made in connection with alterations of laws, and/or due to changes in use areas of transmission apparatus. As a result, for example, in such a case that a frequency band which should be set is changed, a band rejection filter must he newly added to a transmission apparatus. That is, since there are some cases that circuit arrangements of transmission apparatus must be changed, there is such a problem that these transmission apparatus cannot be properly adapted to the changed restricted contents in a flexible manner.
More specifically, in power line communications (PLC), there are some possibilities that these power line communications utilize frequency bands which are used by the presently existing communication systems, for example, amateur radio communications and shortwave broadcasting. As a result, it is required to avoid interference occurred between these presently existing communication systems and the above-described power line communications, so that various sorts of limitations have been made as to contents of restrictions such as frequency bands and allowable electric field strengths. As a consequence, even in such a case that the above-explained various sorts of limitations have be additionally conducted to the restricted contents, such transmission apparatus capable of being properly adapted in a flexible manner to changes in characteristic values which should be set has been desirably expected.
A problem to be solved is given as follows: That is, in the case that a characteristic value is changed which should be set as to a transmission signal, since a circuit arrangement of a transmission apparatus must be changed, the transmission apparatus cannot be properly adapted to the change in the characteristic value to be set in a flexible manner.